Voltage sampling, amplifying, and combining cathode ray tube system



1964 c. J. CARTER 3,153, 73v

VOLTAGE SAMPLING, AMPLIFYING, AND cousmmc CATHODE RAY was: sYs'rEM Filed March so. 1961 l4 2 FIG. I. i;

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INVENTOR Clarence J. Carter ATTORNEYS United States Patent 3,153,173 VQLTAGE SAMPLING, AMPLMYWG, AND COM- BHNEJG CATHOHE RAY TUhE SYSTEM Clarence .1. Carter, Rolling Hills, (3%., assignor, by

mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Mar. 30, 1961, Ser. No. 99,439 2 Claims. (Cl. 315-21) This invention relates to an improved system for sequentially or selectively sampling a large number of very low voltage input signals at a high rate of sampling and amplifying and combining the signals on a single channel.

The system of the present invention makes use of a beam switching tube and constitutes an improvement over the system invented by Menno Wolf. In the system invented by Wolf an electron beam is scanned over a conducting plate having a plurality of apertures defined therein. The electron beam is controlled so that it is directed sequentially through each of the apertures in the plate. The aperture plate is biased at anode potential. A pair of parallel rod-shaped electrodes are mounted behind each aperture in the aperture plate and a different input signal is applied to each pair of rod-shaped electrodes. Behind the pairs of rod-shaped electrodes is a collector plate and this collector plate is also biased at anode potential. A single output channel is connected to this collector plate. The electron beam, upon passing through one of the apertures in the aperture plate, will pass between a pair of rodshaped electrodes to the collector plate. The pair of rodshaped electrodes between which the beam passes will modulate the current of the beam in accordance with the signal applied thereto. Thus as the beam is directed sequentially through the apertures, the current flowing from the collector plate will vary as a function of the samples of the input signals in accordance with the sequence with which the beam is directed through the apertures.

The system of the present invention is similar to the above described system of the prior art but provides a greater amplification of the input signals and thus permits smaller input signals to be sampled. Also in the system of the present invention the collector plate is eliminated, the construction of the control electrodes mounted behind the apertures is simplified, and the positioning of the control electrodes behind the apertures is less critical. All of these features substantially reduce the cost of manufacture of the tube.

According to the present invention the control electrodes which are positioned behind the apertures are in the shape of conducting cups having their open ends facing the apertures so that electrons from the electron beam passing through one of the apertures will pass into space within one of the cups. These cup-shaped control electrodes are biased at cathode potential. The signal potential is added to this cathode potential making each of the control electrodes slightly more negative than anode potential by an amount proportional to the input signal. The electrons of the electron beam Will have different velocities and some of them will be deflected back to the aperture plate and some will be collected by the control electrodes. The amount of each will vary with the applied input signal, thus the current from the aperture plate or the combined current from the control electrodes will be amplified samples of the input signals in accordance with the sequence in which the electron beam is directed through the apertures of the plate. Because the control electrodes are opaque to the electron beam, because the control electrodes are biased at cathode potential, and because the velocity spectrum of the electron beam is relatively narrow, a large amplification of the input signals will be obtained. The signal sensitivity is limited only by the noise 3,153,173 Patented Oct. 13, 1964 of the beam. By means of this system, voltage differences of less than a millivolt are easily detectable.

The feature of applying a bias at cathode potential to the control electrodes and adding the input signals to this cathode potential is a method of operation which could be applied to the Wolf apparatus to obtain improved amplification. The amplification would not be as. great, however, as is obtained with the apparatus of the present invention because the electrodes of the Wolf apparatus are not opaque to the electron beam and they are not cup shaped.

Embodied in the concept of the present invention is a novel amplifier tube. If the electron beam is directed continuously on one of the apertures and an input signal applied to the control electrode, an amplified output will be obtained. If the tube is to be used only as an amplifier, only one aperture and one control electrode is needed.

Further objects and advantages of the present invention will become readily apparent as the following detailed description of a preferred embodiment of the invention unfolds and when taken in conjunction with the drawings wherein:

FIGURE 1 schematically illustrates the system of the invention, and

FIGURE 2 illustrates the details of the electron dynamics around one aperture and control electrode with the beam directed toward this aperture.

The invention makes use of an electron beam tube, in which an electron beam is generated by an electron gun as in a conventional cathode ray tube. An electron gun has a cathode from which electrons are emitted and an anode which accelerates the electrons emitted from the cathode to form the electron beam. In the specification and claims cathode potential shall be defined as that potential applied to the cathode of the electron gun and anode potential shall be defined as that potential applied to the anode of the electron gun.

In-FIGURE 1 the electron gun is designated generally by the reference number 11 and the electron beam is designated by the reference number 10. The electron beam is directed generally inthe direction of a conducting plate 12. The specific direction of the electron beam 10 is controlled by the deflection plates 13 in the manner of a cathode ray tube. The plate 12 has a plurality of regularly arranged apertures 14 defined therein and distributed uniformly thereover. In back of each'of the apertures 14 is mounted a control electrode 15. These control electrodes 15 are in the shape of cups with their open ends facing the apertures 14 in the plate 12. The control electrodes 15 are made of conducting material and are constructed to be opaque to the electron beam 10. In operation, the conducting plate 12 is biased at anode potential and the control electrodes 15 are biased near cathode potential by variable battery 19. The input signals are in the form of small negative potentials and are each applied to a different one of the control electrodes 15. The total potential applied to each of the control electrodes 15 will be the cathode potential plus the signal potential ap plied to such electrode. The signal potentials are small relative to the cathode potential so that each of the control electrodes will be near cathode potential.

The deflecting plates 13 are operated to direct the electron beam at the apertures 14, one at a time. The electron beam Will then pass through the aperture at which it is directed. Some of the electrons will be deflected back to the plate 12 and some will continue on to be collected by the control electrode 15 behind the aperture. The number of electrons which are deflected back to the plate 12 and the number which proceed on to the control electrode 15 is a function of the signal potential applied to the control electrode and thus the resulting current flowing .3 from either the control electrode or the conducting plate 12 is a function of this signal potential.

FIGURE 2 illustrates the electron dynamics in detail which take place when an electron beam is directed through an aperture 14. The electrons of the electron beam will not all be traveling with the same velocity because they will be emitted from the cathode of the electron gun with different thermal energies. The electron beam will have a velocity spectrum with the velocities of the electrons of the electron beam varying over a narrow range. When the electrons of the electron beam pass through an aperture 14, the lower velocity electrons will have insufiicient kinetic energy to overcome the field produced by the potential applied to the control electrode. These low velocity electrons will be deflected to and collected by the conducting plate 12 which is at anode potential. The higher velocity electrons, however, will have enough energy to overcome the potential of the control electrode 15 and these electrons will pass on to and be collected by the control electrode 15. Because the control electrode 15 is opaque to the electron beam, all of the electrons of the electron beam must either be collected by the plate 12 or the control electrode 15. Because the control electrodes are biased at or near cathode potential, they are biased near the middle of the velocity spectrum of the electron beam. The proportion of electrons which are deflected back will therefore depend upon the signal potential added to this cathode potential and because the velocity spectrum is narrow, a small change in signal potential will cause a relatively large change in this proportion. Thus a small change in input signal will cause a large change in electron current flowing from the control electrode and the plate 12. Therefore, either of these currents will be an amplified function of the input signal.

As shown in FIGURE 1 the electron current flowing from the conducting plate 12 is detected by a load resistor 16 which connects the positive pole of a battery 17 to the conducting plate 12. The battery 17 supplies the anode bias potential to the conducting plate 12. The output signal is taken from the junction of the resistor 16 and the plate 12 by means of a capacitor 18.

In operation, the electron beam may be directed sequentially at each of these apertures 14 in the plate 12 in which case the output signal from the capacitor 18 would be a sequence of amplified samplings of the input signals applied to the plurality of control electrodes 15. Alternatively, the deflecting plates may control the electron beam to be directed at a selected one of the apertures 14 and thus an amplified output signal of any selected one of the plurality of input signals is provided. Thus there is provided a combination amplifier and switch which may be easily adapted to provide a commutated output of a large number of input signals. By means of this system tens of thousands of signal inputs of millivolt levels may be sampled at a rate of a few hundred times per second.

The output signal may be obtained from the electron current flowing from the control electrodes instead of from the plate 12. In this case the current flowing from the control electrodes would be combined into a single channel by means of a conventional summing circuit.

These and many other modifications may be made to the above described system without departing from the spirit and scope of the invention which is limited only as defined in the appended claims.

What is claimed is:

1. Electron beam switching apparatus comprising:

(a) cathode means for generating an electron beam,

(b) a conducting plate having a plurality of apertures defined therein, the plate being spaced from the cathode means so that the electron beam may be directed through any one of the apertures,

(c) a plurality of cup-shaped control electrodes each positioned adjacent a diiferent one of the apertures so that the electron beam may be directed through the associated aperture into the interior of the cup,

(d) means to bias the plate at a potential highly positive relative to the cathode means and the control electrodes, the cathode means and the control electrodes being biased at substantially the same potential,

(e) means to apply input signal voltages separately to each of the control electrodes to change the bias of such electrodes slightly relative to the plate,

(1) and means to derive an output signal from the plate.

2. Electron beam switching apparatus comprising a cathode means for generating electrons, electron beam forming and controlling means for forming electrons from said cathode means, a conducting plate having a plurality of apertures defined therein and positioned so that the electron beam may be directed through any one of the apertures, a plurality of cup-shaped electrodes each positioned adjacent a different one of said apertures having the open end of said cup-shaped electrode to receive said electron beam whenever it is directed through the associated aperture into the interior of the cup, said conducting plate positioned between the electron beam forming and controlling means and the cup-shaped electrodes, potential means to bias the plate at a positive potential relative to the cathode means and the electron beam forming and controlling electrodes, the cathode means and the control electrodes being biased at substantially the same potential, means to apply input signal voltages separately to each of the control electrodes to change the bias of such electrodes slightly relative to the plate, and means to derive an output signal from the plate that is a commutated output of a large number of input signals.

References Cited in the file of this patent UNITED STATES PATENTS 

1. ELECTRON BEAM SWITCHING APPARATUS COMPRISING: (A) CATHODE MEANS FOR GENERATING AN ELECTRON BEAM, (B) A CONDUCTING PLATE HAVING A PLURALITY OF APERTURES DEFINED THEREIN, THE PLATE BEING SPACED FROM THE CATHODE MEANS SO THAT THE ELECTRON BEAM MAY BE DIRECTED THROUGH ANY ONE OF THE APERTURES, (C) A PLURALITY OF CUP-SHAPED CONTROL ELECTRODES EACH POSITIONED ADJACENT A DIFFERENT ONE OF THE APERTURES SO THAT THE ELECTRON BEAM MAY BE DIRECTED THROUGH THE ASSOCIATED APERTURE INTO THE INTERIOR OF THE CUP, 